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Zoology > Development One (Test Two) > Flashcards

Development One (Test Two) Flashcards

1
Q

How did early scientists answer the central question of “how does a single celled zygote become a fully functional organism”?

A

They thought of the idea of pre-formation.

Preformation meant that the being inside was already formed and they pictured it as a miniature adult inside the sperm or egg.

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2
Q

How did Kaspar Friederich Wolff demonstrate that there was no preformed chick in the early egg?

A

He noticed that the undifferentiated granular material became arranged into layers

The layers thickened, thinned, and folded to produce the embryo.

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3
Q

What did Kaspar Friederich Wolff call the process of forming an embryo?

A

He called it epigenesis (origin upon or after)

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4
Q

What did Kaspar Friederich Wolff not know?

A

How the fertilized egg, containing the building material, actually developed.

He didn’t know what directed the process.

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5
Q

How are current ideas of development similar and different to those of Wolff’s?

A

They are similar in that they are essentially epigenetic in concept.

They are different in that we know much more about what directs growth/development, hence the discovery of mitosis.

We now understand cellular diversity as a hierarchy of developmental decisions.

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6
Q

What is key to the definition of Fertilization?

A

The moment of fertilization is when the two gamete nuclei fuse.

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7
Q

What first happens when the sperm finds egg?

A

Firstly, the sperm must penetrate the jelly layer that surrounds the egg.

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8
Q

What happens secondly in the process of fertilization?

A

After penetration of the jelly layer, the sperm contacts the vitelline envelope

The vitelline envelope is a thin layer that is above the egg’s plasma membrane.

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9
Q

What makes sure the sperm is of the same species as the egg?

(Lots of different sperm floating around in the ocean!)

A

The enzymes on the vitelline envelope make sure the sperm is the same species because the sperm’s acrosomal process must have the correct enzymes that match the envelope in order to bind.

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10
Q

What is/are the yolk granules?

A

“Packages of nutritional value”

(inside the egg in the cytoplasm)

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11
Q

What is polyspermy, and how does it affect development?

A

Polyspermy is the entry of more than one sperm to an egg, and it is detrimental to normal development.

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12
Q

What is “fast block”?

A

First, quick, step in prevention of polyspermy

Electrical potential of the membrane changes when a sperm (slightly negative) enters because the inside of egg becomes positively charged, which spreads across the membrane and prevents entry of any other sperm.

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13
Q

What is “slow block”?

A

Second prevention of polyspermy after the fast block, cortical granules on the edge of the plasma membrane release contents between the membrane and the vitelline envelope once a sperm has fused with the plasma membrane.

This creates an osmotic gradient, which causes water to rush into the space and the envelope swells.
This swelling lifts away all the bound sperm, except the one that fused with the membrane.

It also modifies the eggs surface so that other sperm cannot enter.

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14
Q

What happens to the sperm after the sperm and egg membranes fuse?

A

The sperm loses its flagellum, and the nuclear envelope of the sperm breaks apart to allow the chromatin to expand (nucleus gets bigger)

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15
Q

Describe the process of pronuclei fusion.

A

The enlarged sperm nucleus (pro-nucleus) migrates inward to contact the female pro-nucleus, which creates a diploid zygote nucleus

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16
Q

What are three cytoplasmic changes does the new diploid zygote go through to prepare for cleavage?

A
  1. protein synthesis
  2. Constant DNA replication
  3. Cytoplasm repositions stuff to activate or repress certain genes
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17
Q

What is cleavage?

A

Cleavage is a series of uneven mitotic divisions.

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18
Q

What is the Animal-Vegetal Axis?

A

The Animal-Vegetal axis is made up of two poles that establish polarity in the new zygote.

  1. Vegetal pole - contains only yolk at one end
  2. Animal pole - region containing mostly cytoplasm that is near to the nucleus
19
Q

What is a cleavage furrow?

A

Cleavage furrow is the ditch like area where the zygote will divide

20
Q

What affects cleavage?

A
  1. Quantity and distribution of yolk present
  2. Genes that control the symmetry of cleavage
21
Q

Describe Isolecithal eggs.

A

They have very little yolk distributed evenly in the cytoplasm, and cleavage is holoblastic.

The nucleus and cytoplasm are centered in the middle and the yolk surrounds it.

22
Q

Isolecithal eggs are holoblastic, what does this mean?

A

Holoblastic means that the cleavage is a complete cut

Cleavage furrow extend completely through the egg

23
Q

Give a few examples of animals that have isolecithal eggs. (TEMMC)

A
  1. tunicates
  2. echinoderms
  3. mollusks
  4. mammals
  5. cephalochordates
24
Q

Describe Mesolecithal eggs.

A
  1. Has a moderate amount of yolk present in vegetal pole
  2. Cleavage is holoblastic
  3. Occur in amphibians
  4. Has a clear Animal-Vegetal axis
25
Q

Describe Centrolecithal eggs.

A
  1. The yolk is concentrated in the center.
  2. Cleavage is meroblastic
  3. Occurs in arthropods (insects)
26
Q

Centrolecithal eggs are meroblastic, what does this mean?

A

The cleavage furrow does not cut through the yolk at all

Specifically in centrolecithal eggs, cleavage is restricted to the cytoplasmic rim of the egg.

27
Q

Describe Telolecithal eggs.

A
  1. Has visible poles
  2. Yolk is concentrated at the vegetal pole
  3. Cleavage is meroblastic
  4. Found in birds, reptiles, most fish, and few amphibians
28
Q

What forms post-cleavage?

What is the outer layer and the fluid-filled cavity inside called?

A
  1. A cluster of cells resulting from continuous cleavage called a blastula is formed
  2. The layer formed by a single sheet of blastula on the outside is called the blastoderm.
  3. Inside the blastula there is fluid filled cavity called the blastocoel.
29
Q

What generally happens during the gastrula stage?

A

In most animals, development continues to form two or three germ layers from the blastula during the gastrula stage

30
Q

What do diploblastic and triploblastic mean?

A
  1. Diploblastic means two germ layers
  2. Triploblastic means three germ layers
31
Q

What specifically happens to the blastula during gastrulation? (four things)

DRAW PICTURE (CHECK AFTER)

A
  1. One side of the blastula (cluster of cells) invaginates (forms a horse-shoe shape)
  2. The internal cavity of the horseshoe is called the gastrocoel “gastro-cole”
  3. The opening to the new internal cavity is called the blastopore
  4. The entire structure (gastrula) has an outer layer called ectoderm (which covers the blastocoel) and an inner layer endoderm (which covers the gastrocoel)
32
Q

What is a blind or incomplete gut?

A

When the embryonic gut opens only into the blastopore (leading to the gastrocoel)

Cnidarians (ingest food and excrete waste one way)

33
Q

What is a complete gut?

A

Most animals have a complete pathway from the mouth to the anus.

34
Q

What is a protostome, and what is a deuterostome?

A

A protostome is when the blastopore becomes the mouth.

A deuterostome is when the blastopore becomes the anus.

35
Q

True or False are all deuterostomes and protostomes triploblastic?

A

True

36
Q

What third layer forms in triploblastic animals?

A

Mesoderm (middle layer) forms between the endoderm and ectoderm

37
Q

What is a coelom?

A

Coelom is the fluid-filled body cavity surrounded by the mesoderm.

38
Q

What is required of an animal to have a coelom?

A

They must have three germ layers (triploblastic)

39
Q

Explain why are coeloms important (three reasons)?

A
  1. It acts as a hydrostatic skeleton, which resists external pressure (water balloon)
  2. It allows for internal organs to move and grow
  3. It acts as a protective cushion for their internal organs
40
Q

After completion of the coelom, the body has three germ layers, name them.

A

Germ Layers:
1. Ectoderm
2. Mesoderm
3. Endoderm

41
Q

After completion of the coelom, the body forms two cavities, name them.

A
  1. Gut Cavity (gastrointestinal tract)
  2. Fluid-filled coelom (body space)
42
Q

What does the mesoderm around the coelom become?

A

Layers of muscle and internal body parts.

43
Q

What are the six key events in sequential, hierarchical progression of development?

A
  1. Gamete production
  2. Fertilization
  3. Cleavage
  4. Gastrulation
  5. Organogenesis
  6. Growth

Zoology (22 decks)

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